1. Field of the Invention
The present invention relates to a semiconductor laser device and a method of fabricating the same, and more particularly, it relates to a semiconductor laser device including a semiconductor element layer having an emission layer and a method of fabricating the same.
2. Description of the Background Art
A semiconductor laser device including a semiconductor element layer having an emission layer is known in general, as disclosed in Japanese Patent Laying-Open No. 2004-327655, for example. The aforementioned Japanese Patent Laying-Open No. 2004-327655 discloses a nitride semiconductor laser device prepared by growing a nitride semiconductor layer (semiconductor element layer) including an emission layer on the surface (principal surface) of a nitride semiconductor substrate having a dislocation concentration region and a low dislocation region in a state inclined by 0.3° to 0.7° with respect to the crystal orientation of the nitride semiconductor substrate. In this semiconductor laser device, the nitride semiconductor layer is grown in the state inclined by 0.3° to 0.7° with respect to the crystal orientation of the nitride semiconductor substrate so that the surface of the nitride semiconductor layer is parallel (planar) to the surface of the nitride semiconductor substrate, whereby dislocations (defects) in the nitride semiconductor layer propagate perpendicularly to the surface of the nitride semiconductor substrate. In the process of growing the nitride semiconductor layer, therefore, dislocations in a portion of the nitride semiconductor layer located immediately above the dislocation concentration region of the nitride semiconductor substrate can be inhibited from propagation into another portion of the nitride semiconductor layer located immediately above the low dislocation region of the nitride semiconductor substrate. Consequently, the number of dislocations can be inhibited from increase in the portion of the nitride semiconductor layer located immediately above the low dislocation region of the nitride semiconductor substrate.
In the nitride semiconductor laser device according to the aforementioned Japanese Patent Laying-Open No. 2004-327655, however, dislocations of the nitride semiconductor layer propagate perpendicularly to the surface of the nitride semiconductor substrate, whereby dislocations of the low dislocation region of the nitride semiconductor substrate also propagate toward the surface of the portion of the nitride semiconductor layer grown immediately above the low dislocation region. Therefore, it is difficult to further reduce the number of dislocations on the surface of the nitride semiconductor layer, and hence it is also difficult to further reduce the number of dislocations in the nitride semiconductor layer including the emission layer. Thus, light absorption by dislocations is so hard to reduce that it is difficult to further improve the luminous efficiency. Further, it is difficult to further reduce the number of nonradiative centers formed in the emission layer since it is difficult to further reduce the number of dislocations in the emission layer as described above. The nonradiative centers, which are levels where carriers recombine without emitting light, formed in the emission layer increase the threshold current. Thus, it is difficult to further reduce the threshold current.